Treatment and recycling of overspray from the spray application of waterborne coatings

ABSTRACT

A process and apparatus for treating overspray from the spray application of waterborne coatings is provided, which includes at least an electrophoresis separation step (means) for recovering substantially all of solids and higher molecular weight water-soluble components and a second separation step (means) for recovering the remainder. The result of such treatment is a recyclable waterborne coating stream of substantially the same composition as the waterborne coating and a recyclable water stream containing substantially none of the resin or additive parts of the original waterborne coating. The process and apparatus are effective, efficient and relatively simple, and recycling is effected without the use of coagulants, detackifiers and other chemical additives which may complicate the recycling procedure and have a detrimental effect on the so recycled products.

BACKGROUND OF THE INVENTION

The present invention relates generally to a process for spray coatingan object with a waterborne coating and, more particularly, to a processfor the treatment and recycling of overspray resulting from such spraycoating. The present process is applicable in industry in general and,especially, in the automotive industry where car bodies and a widevariety of other larger objects are spray coated.

Efficient coating of automobiles and other larger objects with liquidcoatings normally requires spray application. Current spray applicationtechniques generate a significant amount of overspray and, in order toisolate this overspray from the immediate surrounding environment, thespraying operation is normally conducted in a spray booth.

The overspray occurring, for example, during automobile coating withwaterborne coatings is normally removed from the spray booth by anexhaust air stream and/or absorbed in water (water curtains or cascades)circulated from a catchment tank. When it is considered that in oneautomobile spray booth alone approximately 1-1.5 tons of paints areapplied daily and approximately 20-30% of this is overspray, themagnitude of the resulting waste problem is apparent.

There exist essentially two options with respect to handling this wasteproduct--disposal and/or recycling. Because of the large volumesgenerated, and because of the environmental consequences involved,disposal is a burdensome and very expensive option. Recycling,therefore, becomes the desirable alternative.

Waterborne coatings utilized in general industry, and particularly inthe automotive field, can include a large number of solid and/or liquidcomponents. These components can generally be broken down into threeprimary categories with subcategories as set forth below:

(I) a substantial amount of water;

(II) a variety of resins (generally higher molecular weight organiccompounds) including one or more of water-insoluble, water-dispersibleand/or water-soluble components; and

(III) optionally, a variety of additives including, for example,water-insoluble (e.g. pigments), water-dispersible (e.g., emulsifiers,stabilizers and rheological additives) and/or water-soluble (e.g. lowermolecular weight polar organic co-solvents, acids and amines)components.

The sheer variety of components makes effective treatment and recyclinga difficult task.

The currently practiced recycling procedures for waterborne coatingsrequire the addition of coagulating agents and/or detackifiers to thecollected overspray. The resulting coagulate is extracted bysedimentation, flotation, filtration and/or similar separationprocesses, and subsequently removed from the spraying area. Due to thepresence of the added chemicals, and due to the coagulated form of therecovered product, recycling is a costly and complex process. Inaddition, the chemical additives often affect the properties of anyreclaimed product, and separation of many water-soluble materials, suchas low molecular weight organic cosolvents, acids and amines, remains aproblem.

Various other recycling methods have also been proposed, but none havebeen totally successful. For example, WO82/02543 describes a method forrecovery and recycling of waterborne coating overspray, whereby theoverspray is collected and separated (e.g. by a traveling screen filteror a settling tank) into a low and high solids (e.g. 10-50% solids)fraction. The solids content of the high solids fraction is preferablyadjusted to fall within the range of 5-30% solids (e.g. by the additionof water), then passed in the form of a slurry to a decanter centrifuge,of a type well-known in the art, which further separates the liquid fromthe solids. The solid component is said to comprise about 75 wt %solids, which can be utilized as a base for a reclaimed paint product,or can be further dried for disposal at a landfill. The liquidcomponent, which can be recycled back to the spray booth, is said totypically comprise less than 1 wt % solids. As is clear, the separationmethods described in the reference are generally ineffective forseparating water-soluble components and, especially, the aforementionedlower molecular weight water-soluble components which tend to build upin the recycled water.

U.S. Pat. No. 4,607,592 discloses a method of processing overspray inconjunction with the use of a complicated apparatus and a burdensomeprocedure. Separation is accomplished via a complex and special filterand filtration technique into concentrated and clear water fraction. Theconcentrated fraction is said to contain the solids and water-solublecomponents of the overspray, with the composition of the concentratedfraction being automatically adjusted to meet the composition of thefresh paint. The reclaimed paint is then recycled by adding it to thefresh paint feed.

While it appears from U.S. Pat. No. 4,607,592 that effective separationand recycling can be accomplished through complex and burdensome means,it would be highly desirable to develop a relatively simple yeteffective and efficient recycling method for such waterborne "waste"products which avoids the use of the coagulating and detackifyingchemicals mentioned above, and in addition effectively and efficientlyrecovers all of the components in a form suitable for direct recycling.

SUMMARY OF THE INVENTION

A process has now been discovered which is relatively simple toimplement yet results in an efficient and effective separation of suchoverspray into components directly suitable for recycling.

In accordance with the present invention, there is provided a processfor treating overspray collected from the spray coating of an objectwith a waterborne coating, which waterborne coating comprises:

(A) water,

(B) a resin part including at least one of a water-insoluble,water-dispersible and/or water-soluble component, and

(C) optionally, an additive part including at least one of awater-insoluble, water-dispersible and/or water-soluble component,

which process results in a recyclable waterborne coating stream ofsubstantially the same composition as the waterborne coating and arecyclable water stream containing substantially none of the resin oradditive parts of the waterborne coating, and which process comprisesthe steps of:

(1) collecting at least a portion of the overspray;

(2a) separating the collected overspray into

(i) a concentrated phase comprising

(a) a substantial portion of the water-insoluble components of the resinand additive parts,

(b) a portion of the water-dispersible components of the resin andadditive parts,

(c) a minor portion of the water and

(d) at least a minor portion of the water-soluble components of theresin and additive parts; and

(ii) a dilute phase comprising

(a) a substantial portion of the water and

(b) the remainder of the resin and additive parts not contained in theconcentrated phase;

(2b) electrophoretically separating the dilute phase into

(i) a concentrated fraction comprising

(a) substantially all of the remainder of the resin part,

(b) substantially all of the remainder of the water-insoluble andwater-dispersible components of the additive part, and

(c) at least a portion of the water-soluble component of the additivepart; and

(ii) a water fraction comprising

(a) a substantial portion of the water,

(b) the residue of the resin and additive parts not contained in theconcentrated fraction;

(3) separating the water fraction into

(i) the recyclable water stream and

(ii) a concentrated residue stream;

(4a) recovering the concentrated phase of step (2a);

(4b) recovering the concentrated fraction of step (2b);

(5) recovering the concentrated residue stream of step (3);

(6) generating the recyclable waterborne coating stream by mixing theso-recovered concentrated phase of step (2a), concentrated fraction ofstep (2b) and concentrated residue stream of step (3) in a manner andwith other components necessary to result in a mixture havingsubstantially the same composition as the waterborne coating.

In the above-described process, step (2a) is generally considered to beoptional, especially in the case of waterborne clearcoats which containvery small amounts of water-insoluble components. For pigmented systemsand other systems containing large amounts of solids, however, greaterefficiency can be achieved in the electrophoretic separation step byprior removal of a significant portion of such solids in step (2a).

When step (2a) is not utilized, the process in accordance with thepresent invention comprises the steps of:

(1) collecting at least a portion of the overspray;

(2) electrophoretically separating the collected overspray into

(i) a concentrated fraction comprising

(a) substantially all of the resin part,

(b) substantially all of the water-insoluble and water-dispersiblecomponents of the additive part, and

(c) at least a portion of the water-soluble component of the additivepart: and

(ii) a water fraction comprising

(a) a substantial portion of the water,

(b) the residue of the resin and additive parts not contained in theconcentrated fraction;

(3) separating the water fraction into

(i) the recyclable waste stream and

(ii) a concentrated residue stream;

(4) recovering the concentrated fraction of step (2);

(5) recovering the concentrated residue stream of step

(6) generating the recyclable waterborne coating stream by mixing theso-recovered concentrated fraction of step (2) and the concentratedresidue stream of step (3) in a manner and with other componentsnecessary to result in a mixture having substantially the samecomposition as the waterborne coating.

It should be noted that electrophoresis has been utilized as a means forrecovery and recycling of waste solutions generated from the applicationof waterborne coatings by electrodeposition (see, for example,JP-LO-100135/1974). The application of electrodeposition to therecycling of overspray from spray applied waterborne coatings, however,is not known from this literature nor is it readily apparent because ofthe vastly different considerations in formulating and utilizing spraycoatings versus electrodeposition coatings.

In conjunction with the aforementioned process, an apparatus fortreating overspray produced from the spray coating of an object with awaterborne coating is also provided, which apparatus comprises:

(1a) means for collecting at least a portion of overspray;

(1b) a catchment tank for holding the collected overspray;

(2) electrophoretic separating means, connected to the catchment tank,for electrophoretically separating the collected overspray into

(i) a concentrated fraction comprising

(a) substantially all of the resin part,

(b) substantially all of the water-insoluble and water-dispersiblecomponents of the additive part, and

(c) at least a portion of the water-soluble component of the additivepart; and

(ii) a water fraction comprising

(a) a substantial portion of the water,

(b) the residue of the resin and additive parts not contained in theconcentrated fraction;

(3) means, connected to the electrophoretic separation means, forseparating the water fraction into

(i) the recyclable water stream and

(ii) a concentrated residue stream;

(4) means, connected to the electrophoretic separation means, forrecovering the concentrated fraction;

(5) means, connected to the means for separating the water fraction, forrecovering the concentrated residue stream;

(6) mixing means for generating a recyclable waterborne coating streamfrom the concentrated fraction, the concentrated residue stream andother components necessary to result in a mixture having substantiallythe same composition as the waterborne coating,

wherein the recyclable waterborne coating stream comprises substantiallythe same composition as the waterborne coating, and the recyclable waterstream contains substantially none of the resin or additive parts of thewaterborne coating.

For treating overspray containing relatively large amounts ofwater-insoluble components, the apparatus preferably comprises:

(1a) means for collecting at least a portion of the overspray;

(1b) a catchment tank for holding the collected overspray;

(2a) means, interposed between the catchment tank and an electrophoreticseparation means, for separating the collected overspray into

(i) a concentrated phase comprising

(a) a substantial portion of the water-insoluble components of the resinand additive parts,

(b) a portion of the water-dispersible components of the resin andadditive parts,

(c) a minor portion of the water and

(d) at least a minor portion of the water-soluble components of theresin and additive parts; and

(ii) a dilute phase comprising

(a) a substantial portion of the water and

(b) the reminder of the resin and additive parts not contained in theconcentrated phase;

(2b) electrophoretic separating means, connected to the means forseparating the collected overspray, for electrophoretically separatingthe dilute phase into

(i) a concentrated fraction comprising

(a) substantially all of the resin part,

(b) substantially all of the water-insoluble and water-dispersiblecomponents of the additive part, and

(c) at least a portion of the water-soluble component of the additivepart; and

(ii) a water fraction comprising

(a) a substantial portion of the water,

(b) the residue of the resin and additive parts not contained in theconcentrated fraction;

(3) means, connected to the electrophoretic separation means, forseparating the water fraction into

(i) the recyclable water stream and

(ii) a concentrated residue stream;

(4a) means, connected to the means for separating the overspray, forrecovering the concentrated phase;

(4b) means, connected to the electrophoretic separation means, forrecovering the concentrated fraction;

(5) means, connected to the means for separating the water fraction, forrecovering the concentrated residue stream;

(6) mixing means for generating the recyclable waterborne coating streamfrom the concentrated phase, the concentrated fraction, the concentratedresidue stream and other components necessary to result in a mixturehaving substantially the same composition as the waterborne coating.

Still further, a process for spray coating an object with a waterbornecoating is provided, wherein overspray is generated by the spraycoating, characterized in that the overspray is treated as describedabove to generate the recyclable waterborne coating stream and therecyclable water stream, at least a portion of the so-generatedrecyclable waterborne coating stream is recycled for spray applicationonto the object, and at least a portion of the recyclable water streamis recycled for use in collecting the overspray.

Finally, an apparatus for spray coating an object with a waterbornecoating is provided, which comprises a spray booth, the apparatus fortreating overspray as described above, a means for recycling at least aportion of the so-generated recyclable waterborne coating stream forspray application onto the object, and a means for recycling at least aportion of the recyclable water stream for use in collecting theoverspray.

These and other features and advantages of the present invention will bemore readily understood by those skilled in the art from a reading ofthe following detailed description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic of a spray coating and overspray treatingprocess and apparatus in accordance with the present invention.

FIG. 2 is a more detailed schematic of a spray coating and overspraytreating process and apparatus in accordance with the present invention.

FIGS. 3-5 are schematic representations of various electrophoreticseparation means for use in the spray coating and overspray treatingprocess and apparatus in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated previously, waterborne coatings intended for sprayapplication can comprise a wide variety of solid and liquid componentsin significantly varying amounts. These components can generally beclassified into one of three well-known groups--(A) water, (B) a resinpart and (C) an additive part.

As utilized herein, the resin part (B) includes those materials whichultimately form the polymer network of the film resulting fromapplication and drying of the waterborne coating. The resin partcomprises materials which are generally (but not always) organic innature, which may be solid or liquid, which are substantiallynon-volatile under formulation and application conditions, and which maybe water-insoluble, water-dispersible or water-soluble. These various"binder" components can comprise, for example, a variety of monomeric,oligomeric and polymeric materials which can be physically drying butpreferably contain reactive functionality for crosslinking. In manycases, these binders are crosslinked with the aid of relatively largeamounts of preferably multifunctional compounds which react with thisfunctionality and are, consequently, significantly incorporated into theresulting crosslinked polymer network. These "crosslinking agents"include a wide variety of known monomeric, oligomeric and polymericcompounds and, for the purposes of the present description, areconsidered included in the resin part.

In contrast, curing agents which are utilized in relatively smallamounts to "catalyze" the crosslinking reaction but are notsignificantly incorporated into the polymer network are here consideredas included in the additive part (C), as are other components whichsimilarly are not significantly chemically incorporated into the polymernetwork. The additive part (C) can include a wide variety of organic andinorganic, solid and liquid, water-insoluble, water-dispersible andwater-soluble components such as, for example, pigments, water-miscibleorganic cosolvents, volatile neutralizing agents (e.g. acids andamines), biocides, rheology modifiers, non-reactive emulsifiers andstabilizers, etc.

As a general rule, waterborne coatings intended for spray applicationwill comprise the resin (B) and additive (C) parts in combined amountsranging from about 25 wt % to about 70 wt % based upon the total weightof the waterborne coating, with water consequently making up theremaining wt %.

Referring now to FIG. 1 in more detail, there can be seen a spray booth10 having connected thereto a paint feed line 12, a water feed line 14,a vapor collection line 16 and a liquid collection line 18. The waterfeed line 14 may be connected, for example, to a water curtain (notpictured) or other similar means for collecting overspray, whichcollection means are in general common and well-known in this type ofspray application. In fact, the spray application of waterborne coatingsis in general well-known to those skilled in the art, and this aspectneed not be discussed in further detail.

Referring back to FIG. 1, the collected overspray is passed via lines 16and 18 to a catchment tank 20, where it is held for further processingas discussed below. At this point, the concentration of the variouscomponents can vary widely depending upon the actual operation of thespray booth and means utilized to collect the overspray. In normalpractice, at least water curtains or similar collection means areutilized, which results in a substantial dilution of the resin andadditive parts of the overspray. In the present system, this dilution ispreferred because a portion of the content of catchment tank 20 issupplied via line 22 to spray booth 10 for use in the collection of theoverspray.

In the preferred operation, the concentration of the resin (B) andadditive (C) parts in catchment tank 20 should be maintained within therange of from about 0.5 wt % to about 20 wt % based upon the totalweight contained therein. At this point in the process, the proportionsof the resin and additive parts relative to each other should notsignificantly vary from that of the fresh waterborne coating, with thepossible exception of certain volatile components (e.g. low molecularweight co-solvents, acids and amines) which may evaporate prior tofurther treatment.

From catchment tank 20, the overspray is optionally first passed througha rough separation means (not pictured), such as a 1000 mesh sieve, toremove any large particulate or other foreign matter. Further processingof the overspray can then take one of two courses depending upon thecomposition of the waterborne coating. In one, the overspray is passedvia lines 24a and 24 directly to an electrophoretic separation means 26.In the other, the overspray is passed via line 28 into a firstseparation means interposed between catchment tank 20 andelectrophoretic separation means 26.

If the coating contains significant amounts of solid components, andespecially water-insoluble solids such as pigments, for most efficientoperation of electrophoretic separation means 26 it is preferred thatthe overspray first be passed via line 28 into first separation means30, which is capable of separating out a substantial portion of thesewater-insoluble components and at least a portion of thewater-dispersible components of (B) and (C).

First separation means 30 can take any one of a number of formswell-known for separating solids from liquids such as, for example,settling tanks, centrifuges, sedimentation filters and the like, as wellas combinations thereof. Of these various well-known options, it ispreferred to utilize at least a centrifuge, such as a horizontalcentrifuge equipped with a screw conveyor.

The result of this first separation step is

(i) a concentrated phase of preferably less than 50% by weight, and morepreferably less than 35% by weight (based upon the total weight of theconcentrated phase) of water, which concentrated phase includes:

(a) a substantial portion of the water-insoluble components of (B) and(C),

(b) a portion of the water-dispersible components of (B) and (C),

(c) a minor portion of the water and

(d) at least a minor portion of the water-soluble components of (B) and(C); and

(ii) a dilute phase including:

(a) a substantial portion of the water and

(b) the reminder of (B) and (C) not contained in the concentrated phase.

The concentrated phase is then passed via line 32 to a recovery means 34(e.g. a mixing tank), which in FIG. 1 is utilized for recovery of thevarious components of (B) and (C) separated from the overspray, as wellas the reformulation of these so-recovered components into a recyclestream 36 which can be recycled in combination with a fresh waterbornecoating stream 38 as the paint feed (paint feed line 12). These aspectsare discussed further below.

The dilute phase, which my still contain significant amounts of many ofthe components of (B) and (C), is then passed via lines 24b and 24 toelectrophoretic separation means 26.

Electrophoretic separation means 26 is based upon electrophoresiscoatings principles which are well-known to those skilled in the art andneed not be explained here in detail. Further detailed information inthis respect can be found by reference to any number of well-knownliterature sources such as, for example, Willibald Machu,Elektrotauchlackierung, Verlag Chemie, Weinheim 1974.

In general terms, electrophoretic separation means 26 comprises a bath26a which is provided with an electrode 26b and a source of electriccurrent 26c. Depending upon the components of the overspray, electrode26b can be utilized as an anode (for components containing anionicgroups such as carboxyl groups) or a cathode (for components containingcationic groups such as amine groups). Upon application of the electriccurrent, substantially all of (B) and (C) are deposited on electrode26b, leaving substantially clean water in bath 26a. The only exceptionis that the lower molecular weight water-soluble additives, such asorganic co-solvents, acids and amines, tend to remain in solution andare only removed at this point to a minor extent.

The result of the electrophoretic separation step is a concentratedfraction comprising:

(a) substantially all of the remainder of (B),

(b) substantially all of the remainder of the water-insoluble andwater-dispersible components of (C), and

(c) at least a portion of the remainder of the water-soluble componentof (C); and

a water fraction comprising:

(a) a substantial portion of the water,

(b) the residue of (B) and (C) not contained in the concentratedfraction.

The concentrated fraction from the electrophoretic separation step canbe recovered, for example, by removing electrode 26b from bath 26a, thencleaning the deposited material from the surface of electrode 26b. Thiscan be accomplished in any number of ways, such as by scraping and/orsoaking the electrode in a diluted solution of the original waterbornecoating. The so-recovered concentrated fraction is then passed via line40 to recovery means 34 for further processing.

The water fraction, now comprising only very small amounts of (B) and(C) contained in the original overspray, and preferably less than 1.0 wt% based upon the total weight of the water fraction, is then furtherprocessed by passing it via line 42 to a second separation means 44,where substantially the rest of these other components are removedleaving a relative high purity water stream 46 which can, for example,be recycled back via line 48 to catchment tank 20, or which can besafely and easily disposed of. Prior to recycling of water stream 46, itis preferably passed by an ultra-violet light source 50 to preventbacteria build-up in the system.

Second separation means 44 can take any one of a number of formswell-known for separation of solutions (separation on a molecular level)such as, for example, ultra- or reverse osmosis filtration. Again, theseseparation means are well-known to those skilled in the relevant art,and need not be discussed further here.

The concentrated residue stream produced from this separation step ispassed via line 52 to recovery means 34.

Recovery means 34, therefore, will contain all of the recoveredcomponents of (B) and (C) from the overspray plus some water carriedtherewith. Because there has been no chemical treatment of theoverspray, the recovered components are essentially in the same state ascontained in the original waterborne coating, although relativeconcentrations my vary. In order to make the mixture suitable forrecycling, that is, substantially the same composition as the originalwaterborne coating, the necessary components can be added via make-upline 54 and mixed into the system by well-known waterborne coatingformulating techniques.

The result, as indicated above, is a recyclable paint stream ofsubstantially the same composition as the original waterborne coating,which can be recycled via line 36 and combined with fresh waterbornecoating from line 38 for spray application.

Referring now to FIG. 2, there is shown a more detailed representationof a recycling process and apparatus in which a spray booth 60 isconnected to a catchment tank 62 to hold the collected overspray 69,catchment tank 62 being provided with a stirring means 61.

Catchment tank 62 is further connected to a separation means 65 such asa centrifuge as mentioned earlier, which substantially separates thesolid components of the overspray from the other components thereof. Theresulting stream which is substantially free of solid components is thenpassed to an intermediate tank 66 and then to a concentrate tank 64equipped with a stirrer 61. Concentration tank 64 is in turn connectedto an ultrafiltration means 63 and an electrophoretic separation means70.

The electrophoretic separation means 70 in accordance with FIG. 2 alsoutilizes the well-known principle of electrophoretic coating, thedeposition process being controlled to such an extent that on thedeposition surface 73 of electrophoretic separation means 70 a loosepaint layer forms which is easily removable, e.g., via mechanical means74 such as a scraper.

The particular construction of the electrophoretic separation means 70of FIG. 2 is generally characterized by an electrophoresis bath 71(equipped with a stirrer 61) for receiving the stream 70a fromconcentrate tank 64, an electrode 67 (72) suspended in bath 71 and, asthe reciprocal electrode 68, a rotating deposition surface 73 which hasin adjoining arrangement one or more mechanical scraper elements 74 toremove the paint material adhering to deposition surface 73, suchremoved paint material 59 being consigned to a separate recovery tank71a.

For optimum processing, it is important that the liquid currents in theelectrophoresis bath 71 are influenced to such an extent that in thearea of the electrodes 67 and 68 neither foam formation nor anaccumulation of paint material results, and that electrophoresis bath 71be cooled at least in the area of electrodes 67 and 68.

Since practice has shown that optimum paint deposition conditions arematerial-specific, the relevant settings and/or adjustments must be madefor the deposition time, the amount of and allowed ripple in the applieddirect current as well as the current limits and pH-value control byamine addition or the like.

Demineralized water is preferably utilized in the process (e.g., for thewater curtain) for the reasons and advantages as described in DE-OS-8300(which is incorporated by reference).

Further, as can be seen from FIG. 2, it is preferred to recycle thewater obtained in the various separation steps back to the spray boothwater system.

As shown in FIGS. 3 to 5, a number of alternative constructions can beprovided for the deposition surface 73 and mechanical scraper elements74 including the following;

a. A parallel arrangement of e.g. plates 75 which periodically immersein bath 71 and which pivot together with the scraper 74 to the recoverytank 71a (FIG. 3).

b. Rotating discs 75a immersed in bath 71 according to FIG. 4, wherebythe scraper 74 also acts as a run-off surface for paint material 59.

c. Configuration as described under b.; utilizing however a rotatingroller as alternative deposition surface (not pictured).

d. A rotating endless steel band 75b as deposition surface 73, arrangedvertically or inclined in, and partially projecting from, bath 71, witha corresponding scraper 74 having a run-off surface to paint recoverytank 71a (FIG. 5).

In addition, a degree of surface roughness on the deposition surfaces toimprove adhesion of the paint material can be advantageous, as can alsothe provision of (not pictured) drying elements such as warm-air jets,infra-red lamps or the like in the area of the deposition elements notimmersed in the electrophoresis bath.

Finally, warming of the bath caused by the electric current has to becounter-balanced and the necessary cooling of bath 71 results fromcooling elements assigned to the area of the deposition electrodes67,68; this can be carried out by, for example, internal cooling whenusing a roller 75b as deposition element, or by cooling coils on or inbath 71.

The systems described can be further supplemented by a subsequentdewatering of the paint material after the mechanical scrapingprocedure, for example by squeegee rollers with possible furthertransport of the separated paint material by means of a screw conveyoror the like to a recovery and/or storage tank (not pictured).

The great advantage, as can be seen, is that substantially nothing needbe wasted in the present system since everything can be recycled. Animportant point is that this is accomplished without the need to addpotentially detrimental chemicals to the overspray, which is thecurrently practiced method. Further, the presently described system iseffective and efficient, yet relatively simple in its construction andimplementation.

Only a limited number of preferred embodiments of the present inventionhave been described above. One skilled in the art, however, willrecognize numerous substitutions, modifications and alterations whichcan be made without departing from the spirit and scope of the inventionas limited by the following claims.

We claim:
 1. A process for treating overspray collected from the spraycoating of an object with a waterborne coating, which waterborne coatingcomprises:(A) water, (B) a resin part including at least one of awater-insoluble, water-dispersible and water-soluble component, and (C)optionally, an additive part including at least one of a waterinsoluble, water dispersible and water-soluble component, which processresults in a recyclable waterborne coating stream of substantially thesame composition as the waterborne coating and a recyclable water streamcontaining substantially none of the resin or additive parts of thewaterborne coating, which process comprises the steps of: (1) collectingat least a portion of the overspray in collection means; (2)electrophoretically separating the collected over-spray withelectrophoretic separating means into(i) a concentrated fractioncomprising(a) substantially all of the resin part, (b) substantially allof the water-insoluble and water-dispersible components of the additivepart, if present, and (c) at least a portion of the water-solublecomponent of the additive part, if present; and (ii) a water fractioncomprising(a) a substantial portion of the water, (b) the residue of theresin and additive parts not contained in the concentrated fraction; (3)separating the water fraction into(i) the recyclable water stream and(ii) a concentrated residue stream; (4) recovering the concentratedfraction of step (2); (5) recovering the concentrated residue stream ofstep (3); and (6) generating the recyclable waterborne coating stream bymixing the recovered concentrated fraction of step (2) and the recoveredconcentrated residue stream of step (3) in a manner and with othercomponents necessary to result in a mixture having substantially thesame composition as the waterborne coating of the overspray.
 2. Aprocess according to claim 1, wherein prior to step (2), said processfurther comprises the steps of first separating the collected oversprayinto(i) a concentrated phase comprising(a) a substantial portion of thewater-insoluble components of the resin and additive parts, if present,(b) a portion of the water-dispersible components of the resin andadditive parts, if present, (c) a minor portion of the water and (d) atleast a minor portion of the water-soluble components of the resin andadditive parts; if present, and (ii) a dilute phase comprising(a) asubstantial portion of the water and (b) the remainder of .the resin andadditive parts not contained in the concentrated phase; followed byrecovering the concentrated fraction and treating the dilute phaseaccording to step (2) of claim
 1. 3. A process for spray coating anobject with a waterborne coating which generates an overspray whichcomprises:(A) water, (B) a resin part including at least one of awater-insoluble, water-dispersible and water-soluble component, and (C)optionally, an additive part including at least one of awater-insoluble, water-dispersible and water-soluble component, whereinthe overspray is generated by said process, and wherein the overspray istreated in accordance with the process of claim 1 or claim 2 whichprocess comprises the steps of recycling, at least a portion of theso-generated recyclable waterborne coating stream for spray applicationonto the object, and recycling at least a portion of the recyclablewater stream for use in collecting the overspray.
 4. An apparatus fortreating overspray produced from the spray coating of an object with awaterborne coating which comprises:(A) water, (B) a resin part includingat least one of a water-insoluble, water-dispersible and/orwater-soluble component, and (C) optionally, an additive part includingat least one of a water-insoluble, water-dispersible and water-solublecomponent,which apparatus comprises: (1a) means for collecting at leasta portion of the overspray; (1b) a catchment tank for holding thecollected overspray; (2b) electrophoretic separating means, connected tothe catchment tank, for electrophoretically separating the collectedoverspray into(i) a concentrated fraction comprising(a) substantiallyall of the resin part, (b) substantially all of the water-insoluble andwater-dispersible components of the additive part, if present and (c) atleast a portion of the water-soluble component of the additive part; and(ii) a water fraction comprising(a) a substantial portion of the water,(b) the residue of the resin and additive parts not contained in theconcentrated fraction; (3) means, connected to the electrophoreticseparation means, for separating the water fraction into(i) a recyclablewater stream and (ii) a concentrated residue stream; (4b) means,connected to the electrophoretic separation means, for recovering theconcentrated fraction; (5) means, connected to the means for separatingthe water fraction, for recovering the concentrated residue stream; (6)mixing means for generating a recyclable waterborne coating stream fromthe concentrated fraction, the concentrated residue stream and othercomponents necessary to result in a mixture having substantially thesame composition as the waterborne coating, wherein the recyclablewaterborne coating stream comprises substantially the same compositionas the waterborne coating, and the recyclable water stream containssubstantially none of the resin or additive parts of the waterbornecoating.
 5. An apparatus according to claim 4, wherein the apparatusfurther comprises:means, interposed between the catchment tank and anelectrophoretic separation means, for separating the collected oversprayinto(i) a concentrated phase comprising(a) a substantial portion of thewater-insoluble components of the resin and additive parts, if present,(b) a portion of the water-dispersible components of the resin andadditive parts, if present, (c) a minor portion of the water and (d) atleast a minor portion of the water-soluble components of the resin andadditive parts, if present; and (ii) a dilute phase comprising(a) asubstantial portion of the water and (b) the remainder of the resin andadditive parts not contained in the concentrated phase.
 6. An apparatusfor spray coating of an object with a waterborne coating whichcomprises:(A) water, (B) a resin part including at least one of awater-insoluble, water-dispersible and/or water soluble, component, and(C) optionally, an additive part including at least one of awater-insoluble, water-dispersible and water-soluble component; whichapparatus comprises a spray booth having connected thereto the apparatusfor treating overspray as set forth in claim 4 or claim 5, means forrecycling at least a portion of the so-generated recyclable waterbornecoating stream for spray application onto the object, and means forrecycling at least a portion of the recyclable water stream for use incollecting the overspray.
 7. The apparatus according to claim 6, whereinthe electrophoretic separation means comprises an electrophoresis bath,an electrode and a reciprocal electrode as deposition surface suspendedin the electrophoresis bath, mechanical means in adjoining arrangementto the reciprocal electrode for removing a paint layer formed on thereciprocal electrode, and a recovery tank for receiving the paint layerremoved from the reciprocal electrode by the mechanical means.
 8. Theapparatus according to claim 7, wherein the deposition surface comprisesa parallel arrangement of plates which pivot together with a scraper asthe mechanical means to the recovery tank.
 9. The apparatus according toclaim 7, wherein the deposition surface comprises a rotating discpartially immersed in the electrophoresis bath, whereby the mechanicalmeans is arranged so that it acts as a run-off surface to the recoverytank.
 10. The apparatus according to claim 7, wherein the depositionsurface comprises a rotating roller partially immersed in theelectrophoresis bath, whereby the mechanical means is arranged so thatit acts as a run-off surface to the recovery tank.
 11. The apparatusaccording to claim 7, wherein the deposition surface comprises avertical or inclined endless steel band partially immersed in theelectrophoresis bath, whereby the mechanical means is arranged so thatit acts as a run-off surface to the recovery tank.
 12. The apparatusaccording to claim 7, wherein the surface of the deposition surfacepossesses sufficient roughness to improve adhesion of the paint layerdeposited thereon.
 13. The apparatus according to claim 7, whereincooling elements are further provided in the electrophoresis bath in thearea of the electrode and reciprocal electrode.
 14. The apparatusaccording to claim 7, wherein drying elements are further provided inthe area of the reciprocal electrode not immersed in the electrophoresisbath.